Generally, a direct current relay or a magnetic switch is a type of electric circuit switching device capable of executing a mechanical driving using a principle of an electromagnet, and capable of transmitting a current signal. The direct current relay or the magnetic switch is installed at various types of industrial equipment, machines, vehicles, etc.
Especially, an electric vehicle such as a hybrid car, a fuel cell car, a golf cart and an electronic forklift is provided with an electric vehicle relay for supplying power of a battery to a power generator and electric components or disconnecting power supply thereto. Such an electric vehicle relay is a very important core component of an electric vehicle.
FIGS. 1 and 2 are views illustrating a structure of a direct current relay in accordance with the conventional art, in which FIG. 1 illustrates an interrupted state (‘OFF’ state) and FIG. 2 illustrates a conducted state (‘ON’ state).
The conventional direct current relay includes: a pair of fixed contacts 2 fixedly-installed at an upper side of an arc chamber 1; a movable contact 3 installed in the arc chamber 1 so as to be linearly moveable, and moveable to contact or to be separated from the pair of fixed contacts 2; an actuator (A) installed below the arc chamber 1, and configured to linearly-move the movable contact 3; and a contact spring 4 configured to obtain a contact pressure of the movable contact 3.
The actuator (A) includes: a coil 5 configured to generate a magnetic field when an external power is applied thereto; a fixed core 6 fixedly-installed in the coil 5; a moving core 7 installed below the fixed core 6 so as to be moveable up and down; a shaft 8 having a lower end fixed to the moving core 7 and having an upper end slidably-coupled to the movable contact 3; and a return spring 9 installed between the fixed core 6 and the moving core 7, and configured to return the moving core 7 to a direction which becomes far from the fixed core 6. The shaft 8 is guided to slide through a shaft hole formed at a central part of the fixed core 6.
An operation of the conventional direct current relay will be explained as follows.
Firstly, an ‘ON’ operation of the conventional direct current relay will be explained.
If a current is applied to the coil 5 in an interrupted state shown in FIG. 1, a magnetic field is generated around the coil 5, and the fixed core 6 is magnetized within the magnetic field. The moving core 7 is upward moved by a magnetic suction force of the fixed core 6, with compressing the return spring 9. Further, the shaft 8 coupled to the moving core 7 is upward moved with compressing the contact spring 4, thereby upward-moving the movable contact 3 to contact the movable contact 3 to the fixed contact 2. As a result, a main circuit is in a conducted state. That is, the main circuit is in a conducted state as shown in FIG. 2.
However, in this case, as the moving core 7 and the fixed core 6 collide with each other, noise is generated.
Next, an ‘OFF’ operation of the conventional direct current relay will be explained.
If an interruption signal is generated in a conducted state shown in FIG. 2, a current flowing on the coil 5 is interrupted and a magnetic field disappears. As a result, the magnetic suction force of the fixed core 6 is removed. Accordingly, the moving core 7 is rapidly downward-moved by a restoration force of each of the return spring 9 and the contact spring 4. Further, as the movable contact 3 is separated from the fixed contact 2 while the shaft 8 is downward moved, the main circuit is in an interrupted state as shown in FIG. 1.
However, the downward movement of the shaft 8 is stopped as a protrusion 8a formed at an intermediate part of the shaft 8 collides with a plate la or a pad plate 1b. In this case, noise is generated due to an impact.
Quality of the direct current relay may be degraded due to noise generated when the moving core 7 and the fixed core 6 collide with each other during an ‘ON’ operation, and noise generated when the shaft 8 and the plates 1a, 1b collide with each other during an ‘OFF’ operation.